Generally a metal Pattern on active layer top is utilized as a mask at heavily doped region in the tanditional Low Temperature Poly-silicon (LTPS), and then an activation process is performed after doping finished.
A schematic figure of a manufacturing method of the tranditional away substrate is shown as FIG. 1. After deposing a buffer layer 112 and a Poly-Silicon layer (Poly) 113 sequentially, turning into demanding patterns by exposure, development, etching, and then further performing with excimer laser annealer (ELA). Next, depositing a gate insulator (GI) 114, depositing a first metal layer (Metal 1) 115 on the top of the GI, etching patterns in demand, revealing a doping-needed part on the Poly layer, covering the no-doping-needed part of the Poly later 113 via utilizing the first metal layer 115, and doping directly to form a heavily doped region 116. The activation process is performed in high temperature after performing heavily doping to form ohmic contact achieving from a semiconductor layer and a metal layer (a source/a drain) and then increase conductivity of the Thin Film Transistor. Because the activation temperature is higher and the first metal layer 115 has been deposited as gate on the substrate at the same time, an adoptable material for the first metal layer 115 should be thermostable. An inter layer dielectric (ILD) layer 117 is deposited after performing activing, etched the patterns in demand, and then reveal the Poly layer 113 where needs to contact with metal. A second metal layer (Metal2) is further deposited to form a Source/a Drain. Finally, an indium tin oxide (ITO) transparent bottom conductivity film 119, a passivation layer 120 and a ITO top thin film 121 are deposited sequentially.
Because the activation temperature is higher and a better thermostability for a metal layer is required, generally Molybdenum (Mo) is applied for a metal under the active layer; however, the resistance for metal Mo is very high to be applied as a conductive metal material, and the RC delay is occurred seriously because of signal wires made of the metal Mo so that affecting reliabilities of image displays and even counting against large sizes for products.